An explosion at the headquarters complex of the Mexican state oil monopoly killed at least 14 people and injured 80 others Thursday afternoon, the company says.The cause has not been confirmed. Local media reported that machinery exploded in the basement of an administrative center next to the 52-story Pemex tower in Mexico City.The blast happened in the B2 building, Pemex said on Twitter. "There are injuries and damage on the ground floor and mezzanine," it wrote.Before the blast, Pemex announced it had evacuated the building because of electrical problems.Interior Department spokesman Eduardo Sanchez confirmed to the Associated Press that the blast occurred in the basement garage of the office tower, where several thousand people work.AP reports that the blast blew out windows on three floors of the auxiliary building.One worker on the 10th floor described to NPR "an amazing explosion" and being thrown from his chair.